This invention relates to an engine and more particularly to an improved management system and control method for such engines.
In many forms of internal combustion engines, there are times when the engine is operated with less than its total number of cylinders running. That is, during the operation of the engine, one or more cylinders may be intentionally disabled and prevented from undergoing combustion. This is done for a variety of purposes.
For example, it has been the practice at times to limit the maximum power output of an engine and to improve its efficiency under some running conditions by disabling certain cylinders. The disabled cylinder or cylinders are prevented from undergoing combustion either by intentionally not firing or misfiring the spark plugs and/or by selectively disabling the supply of fuel to those cylinders. This permits the engine to operate as a variable displacement engine. Thus only the displacement necessary for any given running condition is employed. This permits increases in the overall efficiency.
This same technique is utilized with engines to permit them to continue to propel the vehicle, but under a reduced speed in the event of some malfunction in the engine. These so called "limp home" modes of operation protect the engine from serious damage, but nevertheless permit the occupants to reach a location where assistance can be obtained.
Another use for such cylinder disabling is disclosed in the copending application of Kazuhiro Nakamura and Kimihiro Nonaka entitled "Combustion Control System for Internal Combustion Engine," U.S. Ser. No. 08/299,517, filed Sep. 1, 1994, assigned to the assignee hereof, now U.S. Pat. No. 5,579,736. In that application, the engine is operated so that the throttle valve is positioned in a substantial partially opened condition under idle and off idle conditions. This improves the performance of the engine on acceleration.
That is, the throttle valve is held more fully opened than with conventional engines so that the engine could induct more air than is necessary for its operation at the idle or off idle speed. The actual engine speed is controlled to the desired speed by selectively disabling one or more cylinders of the engine. The actual number of cylinders disabled will be determined by the actual desired speed for the engine. This system significantly improves engine performance.
With the systems, however, if the engine speed is controlled solely in response to the existing engine speed, there may be situations where the engine speed control results in a less than desired result. For example, this type of control has particular utility in conjunction with two-cycle engines and particularly utilized with outboard motors. Outboards, however, have a particularly running environment which is not typical with other types of engine powered vehicles.
That is, an outboard motor is frequently operated at an idle speed in a neutral condition. However, the engine also is operated in a trolling condition when the actual speed of the engine is less than the idle speed. Therefore, if the engine is operating in idle and its speed has been controlled by reducing the number of cylinders, when shifting into gear for trolling operations stalling may occur.
It is, therefore, a principal object of this invention to provide an engine control that is sensitive not only to the running condition of the engine but also other extraneous conditions which may change the load on the engine.
It is a further object of this invention to provide an improved engine and control that may be utilized in a vehicle wherein the engine speed control is also sensitive to the vehicle condition and the drive condition between the engine and the vehicle.
It should be noted that, although reference is made to "cylinders" the same principles may be applied to rotary engines. Hence the terms "cylinders" or "combustion chambers" as used herein are intended to encompass either reciprocating or rotary engines, unless otherwise so specified.